Some shipping cartons are manufactured with the closure flaps folded downwardly along the sides and ends of the cartons. The flaps are maintained in the open downturned position along the sides of the carton by short integral paperboard strips or webs which connect the side flaps and end flaps at diagonally opposite corners of the carton. The flaps thus do not extend outwardly and the cartons are more easily handled during filling operations. To close the flaps after the carton is filled, the attaching webs between the end and side flaps are slit or severed to enable folding of the flaps to the closed position over the top of the carton and its contents. Conventional folding apparatus employs folding plows arranged along the sides of the moving carton to flip the flaps upwardly and over the top of the carton as the carton is conveyed between the plows. The carton must be shifted 90.degree. to employ such folding plows to flip the end flaps after the side flaps are folded or vice versa. One such arrangement requires two conveyors at right angles. Other apparatus requires bump turning. This arrangement is impractical where there are space limitations in the carton filling facility. U.S. Pat. No. 3,533,214 is illustrative of right angle conveyors to accomplish slitting of flap webs.